首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   824181篇
  免费   96414篇
  国内免费   351篇
  920946篇
  2018年   6946篇
  2016年   9125篇
  2015年   12242篇
  2014年   14759篇
  2013年   20771篇
  2012年   23148篇
  2011年   23532篇
  2010年   15804篇
  2009年   14752篇
  2008年   21121篇
  2007年   21934篇
  2006年   20793篇
  2005年   20050篇
  2004年   19862篇
  2003年   19274篇
  2002年   18582篇
  2001年   38204篇
  2000年   38684篇
  1999年   30430篇
  1998年   10307篇
  1997年   10851篇
  1996年   10213篇
  1995年   9747篇
  1994年   9649篇
  1993年   9683篇
  1992年   25758篇
  1991年   25532篇
  1990年   24866篇
  1989年   24115篇
  1988年   22467篇
  1987年   21419篇
  1986年   19862篇
  1985年   20027篇
  1984年   16507篇
  1983年   14452篇
  1982年   10887篇
  1981年   10067篇
  1980年   9489篇
  1979年   16083篇
  1978年   12497篇
  1977年   11484篇
  1976年   10698篇
  1975年   12032篇
  1974年   12634篇
  1973年   12508篇
  1972年   11520篇
  1971年   10272篇
  1970年   9094篇
  1969年   8619篇
  1968年   7809篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
995.
The ECF™ lateral flow assay test is marketed to detect non-pregnancy in mares. The objectives of the present study were to determine the accuracy of the ECF test, the accuracy of the electronic reader accompanying the ECF test, and agreement between two human readers and the electronic reader. Serum samples were collected from anestrus, cycling but not inseminated, and inseminated mares, and were evaluated with the ECF™ test (EDP Biotech Company, Knoxville, TN, USA) at The Ohio State University and at the EDP Biotech Laboratory. Specificity ranged from 0.07 to 0.16, the negative predictive value ranged from 0.15 to 0.33, and accuracy ranged from 0.43 to 0.52. The electronic reader did not add improve the accuracy or predictive values of the test. Based on the electronic reader, 80.0% of the serum samples collected from the anestrus mares were false positives; Readers 1 and 2 had 60.0 and 33.3% false positives, respectively. For samples collected during the estrous cycle, 83.9% were false positives by the electronic reader, whereas Readers 1 and 2 had 43.7 and 26.4% false positives. We concluded that, regardless of whether the test strips were evaluated by a human or electronic reader, this assay was not accurate for determination of the non-pregnant mare.  相似文献   
996.
Great skepticism has surrounded the question of whether modulation of voltage-gated Ca2+ channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in CaV2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP2), a palmitoylated accessory subunit (β2a) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M1 muscarinic receptors may stimulate multiple lipases to break down the PIP2 associated with VGCCs and leave PIP2's freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs.  相似文献   
997.
The effects of biological treatments with PlantShield®, Prestop®, Quadra 136, RootShield®, and S33 (Rhodosporidium diobovatum) and chemical treatment with Decree® applied as a preventive or curative sprays on stem canker caused by Botrytis cinerea on tomato plants grown in sawdust were studied under near-commercial greenhouse conditions. Prestop® and Decree®, applied as preventive or curative sprays, PlantShield® applied as curative spray, and S33 and Q-136 applied as preventive or preventive plus one spray to wounded surface provided season-long protection from B. cinerea stem canker. These treatments also increased fruit yield and decreased the number of dead plants compared with the inoculated control.  相似文献   
998.
The combination of alpha interferon and vinblastine has been reported to yield a response rate of 30-40% in previously untreated patients with metastatic renal cell carcinoma. This combination was given to nine patients with advanced metastatic renal carcinoma after they failed or relapsed on alpha-interferon alone, to attempt to evaluate the role of vinblastine in this combination. Neither complete nor partial response was observed. Two patients had disease stabilization for two and seven months. Our preliminary results suggest that vinblastine did not add to the efficacy of interferon in this group of patients.  相似文献   
999.
1000.
It is shown that both intracerebral and intraperitoneal neurotropin administration resulted in a decrease of seizure susceptibility of preliminary picrotoxin--kindled rats. On the other hand, neurotropin did not change the course of kindling development. Under conditions of acute picrotoxin--induced seizures it was observed that preliminary cycloheximide (protein-synthesis blocker) administration abolished anticonvulsant properties of neurotropin. It is concluded that anticonvulsant effects of neurotropin are realized via modulation of endogenous peptides synthesis and, in particular, cerulein.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号